1. Field of the Invention
The present invention relates to a lumbar support device for a vehicle seat and, more particularly, to such lumbar support device in which a cam is rotated to move one end of an elastic member extended across the right and left sides of a back frame of the seat in the longitudinal direction of the elastic member and thus to vary the curvature of the elastic member in its longitudinal direction so that the hardness of the lumbar support section of the vehicle seat can be adjusted.
2. Description of the Prior Art
A conventional lumbar support device of this type is illustrated in FIG. 1. In this conventional device, a plate cam (1) is rotated via a shaft of rotation (4) by turning a handle (3) projected from the side of a seat back, and such rotation of the plate cam (1) causes an elastic member (2) of a wire to be moved in its longitudinal direction to vary the curvature of the elastic member (2) so as to adjust the hardness of the lumbar support section of the seat back. In FIG. 1, reference numeral (5) designates a slide piece which fixes one end of the elastic member (2) and is engaged with the plate cam (1), and (6) represents a seat frame of the seat back.
In such conventional lumbar support device, however, since the loads of the elastic member are carried by one surface of the plate cam, heavy loads are necessary to operate the cam. In other words, such conventional device is disadvantages in that the adjustment of the hardness of the seat back lumbar support section can not be made smoothly.